A fiber optic gyroscope (FOG) uses the interference of light to measure angular velocity. Rotation is sensed in a fiber optic gyroscope using a large coil of optical fiber. To measure angular velocity, two phase modulated light beams are introduced into a coil in opposite directions by an electro-optic modulating device such as an integrated optical circuit (IOC). When the coil is undergoing rotation, a light beam traveling in the direction of rotation will experience a longer path to the other end of the fiber loop than the light beam traveling against the rotation. This is known as the Sagnac effect. As the beams exit the fiber they are combined. The phase shift between the counter-rotating light beams due to the Sagnac effect is a function of the rotational rate of the coil. Thus by evaluating the intensity and phase of the interference of the resulting combined beam, the angular velocity of the coil can be determined.
One material typically used in IOC waveguides for fiber optic gyroscopes is LiNbO3. Lithium niobate does not exist in nature. It is synthesized to create its piezoelectric properties. Modulation of the counter propagating light beams is accomplished by applying a voltage across a portion of the waveguide, which in turn changes the refractive index of the LiNbO3 material. This effect enables phase modulation, φ(t), of the electromagnetic light wave transiting the waveguide. However, a problem has been observed in these fiber optic gyroscopes when operating in non-atmospheric conditions such as a vacuum or near vacuum environment, such as outer space. A phenomenon referred to herein as “ionic migration” occurs in proton exchanged LiNbO3 waveguides operating under non-atmospheric conditions that are exposed to electric fields. This observed “ionic migration” corrupts the electro-optic modulation of light beams, eventually rendering the fiber optic gyroscope inoperable.
For the reasons stated above and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the specification, there is a need in the art for improved fiber optic gyroscopes for operation in non-atmospheric environments.